Defending APIs

Defending APIs

Table of contents

we embark on a journey to fortify our APIs against common vulnerabilities that lurk at every stage of the Software Development Lifecycle (SDLC). Drawing from insights gained through dissecting past breaches and understanding the ramifications of insecure APIs, our focus now shifts to cultivating a defensive mindset aimed at crafting robust and resilient APIs from the ground up.

Throughout the chapters preceding this one, we've delved into the arsenal of techniques attackers employ to compromise APIs, setting the stage for our defensive endeavors. Now, armed with this knowledge, we are poised to confront each class of vulnerability head-on, equipping ourselves with best practices, cautionary tales of common pitfalls, recommendations for essential tools and libraries, and illustrative code samples showcasing key defensive strategies.

For developers, this aticle represents a pivotal milestone in your learning journey, empowering you to architect APIs that not only meet functional requirements but also stand as bastions of security in an ever-evolving threat landscape. Meanwhile, for those seeking a broader understanding of API security, this chapter offers invaluable insights into foundational defensive techniques that underpin the resilience of modern digital ecosystems.

Building upon the critical lessons learned in "Attacking APIs," where we underscored the indispensable role of authentication and authorization in safeguarding APIs, the initial focus of this chapter is to reinforce these fundamental pillars of API security. Fortunately, the path to enhancing authentication and authorization mechanisms is paved with well-established practices, patterns, and readily available supporting libraries, ensuring that API builders can swiftly bolster their defenses against unauthorized access and misuse.

Securely Handling JSON Web Tokens (JWTs) in Your API

JSON Web Tokens (JWTs) have become a cornerstone in modern API implementations, serving as a portable means of exchanging information about identity and permissions. However, their ubiquity also makes them prime targets for various attacks if not handled securely. In this article, we'll explore key strategies for securely handling JWTs within your codebase to mitigate common vulnerabilities.

1. Purposeful Usage of JWTs

First and foremost, ensure that you're using JWTs for their intended purpose – as a means of exchanging information about identity and permissions. Avoid using them as session cookies, as this can lead to issues with logging out users and increases the risk of theft and misuse.

# Avoid using JWT as a session cookie
# Example of incorrect usage
app.use(session({ secret: 'keyboard cat', cookie: { secure: true, maxAge: 60000 }, saveUninitialized: true, resave: true }));

2. Secure Storage Mechanisms

When storing JWTs on the client-side, prioritize secure storage mechanisms to prevent theft via Cross-Site Scripting (XSS) attacks. Utilize browser memory or cache (session storage) for temporary storage, or consider utilizing the HttpOnly tag on cookies to prevent theft.

// Example of storing JWT in session storage
sessionStorage.setItem('jwtToken', token);

// Example of setting HttpOnly flag on cookies
res.cookie('jwt', token, { httpOnly: true });

3. Explicit Declaration of Token Usage

Explicitly declare the intended usage of your token by setting the typ field in the JWT header. This helps in ensuring that the token is used in the correct context and prevents potential misuse.

// Example JWT header with explicit token type
  "alg": "HS256",
  "typ": "IT+JWT",
  "kid": "BTVBRYNjEyxc"

4. Expiration Timestamp Management

One of the crucial properties of a JWT is its expiration timestamp. Ensure that JWTs are generated with appropriate expiration windows and that clients validate these expirations before trusting the token. Determine suitable lifetimes based on the specific application requirements, considering factors such as internal services versus external APIs requiring human login.

// Example of setting expiration timestamp
const token = jwt.sign({ user: 'username' }, 'secret', { expiresIn: '1h' });

Securely Using Algorithms in API Development

In the realm of API security, the choice and implementation of cryptographic algorithms play a crucial role in safeguarding against various attacks. In this article, we'll delve into best practices for securely using algorithms within your API to mitigate vulnerabilities and enhance overall security.

Explicit Algorithm and Key Specification

One of the fundamental principles to thwart potential attacks is to be explicit about the cryptographic algorithm and key used for signing JWTs. By ignoring values supplied in the JWT header and specifying the algorithm and key directly, you eliminate the risk of attackers injecting malicious keys or confusing the client about the algorithm in use.

# Example of explicit algorithm and key specification in JWT generation
jwt.encode({'user': 'username'}, 'secret_key', algorithm='HS256')

Signing and Verification

Always ensure that JWTs are signed upon generation and that the signature is verified upon consumption. This ensures the integrity and authenticity of the tokens, preventing tampering or unauthorized access.

// Example of JWT verification upon consumption
jwt.verify(token, 'secret_key', (err, decoded) => {
  if (err) {
    // Handle verification failure
  } else {
    // Token is valid, proceed with processing

Secure Key Management

When using symmetric keys, such as those in HMAC-based algorithms like HS256, it's imperative to securely manage and distribute these keys. Avoid common pitfalls associated with secret distribution, such as storing keys in plain text or committing them to source code repositories.

# Example of generating a secure random key
openssl rand -base64 32

Utilizing Key Vaults

Consider utilizing a robust key vault solution for managing your cryptographic keys securely. Key vaults provide centralized management, access control, and auditing capabilities, reducing the risk of unauthorized access or accidental exposure of keys.

# Example of using Azure Key Vault for secure key storage
az keyvault secret set --vault-name <vault-name> --name <secret-name> --value <secret-value>

Utilizing Libraries Effectively for JWT Handling

JSON Web Tokens (JWTs) are a popular choice for secure authentication and data exchange in modern web applications. However, proper usage of libraries for JWT generation and consumption is critical to ensure the security and integrity of your system. In this article, we'll explore best practices for using libraries correctly to handle JWTs securely.

JWT Generation in Python

Let's start with a basic example of generating JWT tokens using the jwt library in Python:

import jwt
import time

def signJWT(user_id: str) -> str:
    payload = {
        "user_id": user_id,
        "expires": time.time() + 600  # Token expiration time (10 minutes)
    token = jwt.encode(payload, JWT_SECRET, algorithm=JWT_ALGORITHM)
    return token

This code snippet demonstrates how to generate a JWT token with a specified payload, expiration time, secret key (JWT_SECRET), and algorithm (JWT_ALGORITHM). Ensure that these values are retrieved securely from storage to prevent unauthorized access.

JWT Decoding on the Client Side

On the client side, you'll need to decode and validate the JWT token to ensure its authenticity and integrity:

def decodeJWT(token: str) -> dict:
        decoded_token = jwt.decode(token, JWT_SECRET, algorithms=[JWT_ALGORITHM])
        if decoded_token["expires"] >= time.time():
            return decoded_token
            return None  # Token expired
    except jwt.ExpiredSignatureError:
        return None  # Token expired
    except jwt.InvalidTokenError:
        return None  # Invalid token

This code snippet decodes the JWT token using the same secret key and algorithm. It verifies the signature and checks the expiration time (expires) to ensure the token is still valid. If the token is valid, the decoded payload is returned; otherwise, None is returned.

Secure Usage Patterns

When utilizing libraries for JWT handling, it's crucial to adhere to secure usage patterns:

  • Hardcoded Algorithm and Secret: Avoid extracting algorithm and secret from the JWT header. Instead, use hardcoded values retrieved securely from storage to prevent potential attacks.

  • Validate Headers: When validating JWTs, check for extraneous values in the headers that may have been inserted by attackers or third parties. This can help detect compromises in closed systems.

Enhancing Password and Token Security

Improving password and token security is paramount in ensuring the resilience of authentication mechanisms against malicious attacks. In this article, we'll explore best practices and implementation techniques in both .NET Core and Java to harden passwords and tokens, thereby fortifying your systems against potential vulnerabilities.

Increasing Complexity and Length

The first step in hardening passwords and tokens is to increase both complexity and length. This simple yet effective approach significantly enhances security:

  • Complexity: Incorporate a wide range of characters, including uppercase letters, lowercase letters, numbers, and special symbols, to maximize permutations and resilience against brute-force attacks.

  • Length: Extend the length of passwords and tokens to increase the number of possible characters, thereby exponentially increasing the time required to crack them.

Utilizing Secure Password Storage Solutions

When human users are involved in the authentication process, consider leveraging secure password storage solutions to encourage the adoption of long and complex passwords:

  • Password Managers: Utilize reputable password managers such as 1Password or LastPass to securely store and manage passwords. These solutions not only enhance security but also mitigate user resistance to using complex passwords.

Time to Crack Passwords: A Deterministic Improvement

The time required to crack passwords increases exponentially with complexity and length. As illustrated in the table below (data from 2023), passwords or tokens with a length of 16 or more characters and with complex characters should be resistant within practical reason from common attacks:

Number of CharactersComplexityTime Taken
4Mixed case lettersInstantly
8Mixed case letters28 seconds
12Mixed case letters6 years
14Mixed case letters17,000 years
16Numbers and mixed case letters779 million years
18Numbers and mixed case letters2 trillion years

(Source: Data from 2023)

Using Cryptographically Secure Pseudo-Random Number Generators

To generate passwords and tokens with a high degree of entropy, utilize cryptographically secure pseudo-random number generators. In .NET Core and Java, different methods are available:

.NET Core Implementation

using System;
using System.Security.Cryptography;

public class PasswordGenerator
    public string GeneratePassword(int length)
        const string allowedChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()_+";

        using (var rng = RandomNumberGenerator.Create())
            var result = new char[length];
            var bytes = new byte[length];


            for (int i = 0; i < length; i++)
                result[i] = allowedChars[bytes[i] % allowedChars.Length];

            return new string(result);

Java Implementation


public class PasswordGenerator {
    private static final String ALLOWED_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()_+";

    public String generatePassword(int length) {
        SecureRandom random = new SecureRandom();
        StringBuilder password = new StringBuilder();

        for (int i = 0; i < length; i++) {

        return password.toString();

Securing the Password Reset Process

Ensuring the security of the password reset process is crucial in safeguarding user accounts against unauthorized access and potential breaches. In this article, we'll discuss best practices and implementation techniques for securing the password reset process, with examples in both .NET Core and Java.

Importance of a Secure Password Reset Process

A flawed password reset process can leave user accounts vulnerable to exploitation and compromise. To mitigate these risks, it's essential to design and implement a secure password reset mechanism that adheres to best practices and considers potential threats and vulnerabilities.

Best Practices for Password Reset Processes

Implement the following best practices to enhance the security of your password reset process:

  1. Bounded Time Window: Ensure that the password reset process has a bounded time window from start to finish. On timeout, reset the process entirely and invalidate any tokens or PINs in use.

  2. Trusted Side Channel: Utilize a trusted side channel, such as email, to communicate the reset sequence to the user securely.

  3. Uniform Responses: Provide uniform responses in content and timing, regardless of whether the account exists, to prevent enumeration attacks.

  4. Logging and Tracking: Log and track suspicious reset activity for potential incident detection and response.

  5. Randomized Reset PINs or Tokens: Ensure that reset PINs or tokens are sufficiently random and cannot be easily guessed.

  6. Progressive Rate-Limiting: Implement progressive rate-limiting on the reset request endpoint to prevent brute-force attacks.

  7. Step-Up Process: Enforce additional security factors, such as security questions, if a user performs multiple reset attempts or enters incorrect information.

  8. User Confirmation: Always confirm with the user at the start and end of the process to indicate a reset is in progress, giving them the option to abort if they did not initiate it.

Implementation in .NET Core

.NET Core Example

// Implementation of secure password reset process in .NET Core
// (Pseudocode)

public class PasswordResetController : ControllerBase
    public IActionResult ResetPassword([FromBody] ResetRequestModel resetRequest)
        // Validate reset request
        // Generate a random token or PIN
        // Send reset instructions via email
        // Log reset activity

        return Ok("Reset instructions sent successfully.");

    public IActionResult ConfirmReset([FromBody] ResetConfirmationModel resetConfirmation)
        // Validate reset confirmation
        // Reset user's password
        // Invalidate reset token or PIN
        // Log reset confirmation

        return Ok("Password reset successful.");

Implementation in Java

Java Example

// Implementation of secure password reset process in Java
// (Pseudocode)

public class PasswordResetController {

    public ResponseEntity<String> requestPasswordReset(@RequestBody ResetRequest resetRequest) {
        // Validate reset request
        // Generate a random token or PIN
        // Send reset instructions via email
        // Log reset activity

        return ResponseEntity.ok("Reset instructions sent successfully.");

    public ResponseEntity<String> confirmPasswordReset(@RequestBody ResetConfirmation resetConfirmation) {
        // Validate reset confirmation
        // Reset user's password
        // Invalidate reset token or PIN
        // Log reset confirmation

        return ResponseEntity.ok("Password reset successful.");

Implementing Authentication

Authentication is a critical aspect of securing API endpoints, ensuring that only authorized users can access protected resources. In this article, we'll explore how to handle authentication in code using examples in .NET Core and Java.

Authentication in FastAPI (Python)

In FastAPI, authentication is achieved using dependency injection to inject an authentication handler into the API endpoint handler. Here's an example:

Python Code (FastAPI)

from fastapi import FastAPI, Depends, HTTPException
from import HTTPBearer, HTTPAuthorizationCredentials
from pydantic import BaseModel
from typing import List

app = FastAPI()

# Mock database
posts = []

class PostSchema(BaseModel):
    id: int
    title: str
    content: str

class JWTBearer(HTTPBearer):
    async def __call__(self, request):
        credentials: HTTPAuthorizationCredentials = await super().__call__(request)
        if credentials:
            if not credentials.scheme == "Bearer":
                raise HTTPException(status_code=403, detail="Invalid authentication scheme.")
            if not self.verify_jwt(credentials.credentials):
                raise HTTPException(status_code=403, detail="Invalid token or expired token.")
            return credentials.credentials
            raise HTTPException(status_code=403, detail="Invalid authorization code.")"/posts", dependencies=[Depends(JWTBearer())], tags=["posts"])
async def add_post(post: PostSchema) -> dict: = len(posts) + 1
    return {"data": "post added."}

Authentication in .NET Core

In .NET Core, authentication is often handled using middleware components provided by the ASP.NET Core framework. These components allow for flexible authentication schemes, including JWT (JSON Web Tokens), OAuth, and cookie-based authentication. Let's see how we can implement JWT authentication in a .NET Core web API.

.NET Core Code Example

// Startup.cs

using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.IdentityModel.Tokens;
using System.Text;

public class Startup
    public void ConfigureServices(IServiceCollection services)
        // Configure JWT authentication
        var key = Encoding.ASCII.GetBytes("YourSecretKeyHere");
            .AddJwtBearer(options =>
                options.TokenValidationParameters = new TokenValidationParameters
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    ValidateLifetime = true,
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new SymmetricSecurityKey(key)

        // Other service configurations

    public void Configure(IApplicationBuilder app)

        // Other middleware configurations

This code sets up JWT authentication in the application's startup configuration.

Authentication in Java

In Java, authentication is commonly implemented using frameworks like Spring Security, which provides comprehensive support for securing web applications and APIs. Spring Security offers various authentication mechanisms, including form-based, HTTP Basic, and JWT authentication. Let's see how we can implement JWT authentication using Spring Security.

Java Code Example (Spring Boot)


import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpMethod;

public class SecurityConfig extends WebSecurityConfigurerAdapter {

    protected void configure(HttpSecurity http) throws Exception {
            .antMatchers(HttpMethod.POST, "/api/authenticate").permitAll() // Allow authentication endpoint
            .addFilter(new JwtAuthenticationFilter(authenticationManager()))
            .addFilter(new JwtAuthorizationFilter(authenticationManager()))

    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();

This code configures JWT authentication using Spring Security in a Spring Boot application.

Authentication in Node.js (Express)

In Node.js with Express, authentication can be implemented by adding a middleware function to the call list in the API endpoint handler. Here's an example:

JavaScript Code (Node.js with Express)

const express = require('express');
const app = express();

// Mock database
const secrets = [{ id: 1, name: "Secret 1" }];

// Middleware function for authentication
function isAuth(req, res, next) {
    const auth = req.headers.authorization;
    if (auth === 'password') {
    } else {
        res.status(401).send('Access forbidden');

// API endpoint handler
app.get("/secrets", isAuth, (req, res) => {

// Start the server
const PORT = 3000;
app.listen(PORT, () => {
    console.log(`Server is running on port ${PORT}`);

Leveraging the OpenAPI Specification for Secure API Design

In the realm of API development, security is a paramount concern. Adopting a design-first approach allows developers to integrate security considerations into the very fabric of their APIs. In this article, we'll delve into utilizing the OpenAPI Specification (OAS) to bolster the security of our APIs. But before we delve into the technical details, let's clarify some terminology surrounding API design methodologies.

API-First vs. Design-First vs. Code-First

  • API-First: In an API-first approach, the primary focus is on building APIs as the core product, with user interfaces (UIs) developed around them. Companies like Twilio exemplify this paradigm, where APIs are the primary revenue driver.

  • Design-First: This methodology involves designing APIs using a specification language like Swagger or OAS before writing any code. It emphasizes security by design and is the approach we'll focus on in this article.

  • Code-First: In contrast, the code-first approach involves writing code to implement APIs before formalizing their design. While prevalent, it's considered a legacy approach and lacks the security benefits of design-first methodologies.

Now that we've clarified these terms, let's explore how we can leverage the OAS for secure API design.

Data Modeling with OAS

At the heart of secure API design lies accurate data modeling. The OAS allows us to precisely define data structures using various primitive and complex types. Here's a brief overview of primitive types supported by OAS:

  • string

  • number

  • integer

  • boolean

  • array

  • object

Complex types, such as dictionaries, can also be defined. For example:

    Messages: # Dictionary
      type: object
        $ref: '#/components/schemas/Message'
    Message: # Object
      type: object
          type: integer
          type: string

Here, Messages is a dictionary with string keys and Message objects as values. The $ref directive allows for referencing common definitions, promoting reusability and maintainability.

Combining Schemas

OAS allows for combining schemas using directives like oneOf, anyOf, allOf, and not. For instance:

                - $ref: '#/components/schemas/Cat'
                - $ref: '#/components/schemas/Dog'

This snippet specifies that the request body can be either a Cat or a Dog, but not both. Additionally, the enum directive can be used to constrain values, enhancing data validation.

Ensuring Data Security

By fully specifying data structures in the OAS, developers can mitigate the risk of data exposure and misuse. However, incomplete or ambiguous specifications can leave APIs vulnerable to attack. Tools like the 42Crunch VSCode Swagger editor extension provide invaluable assistance in auditing OAS definitions for security gaps.

Enhancing API Security with the OpenAPI Specification

In the realm of API development, ensuring robust security measures is paramount to protect sensitive data and prevent unauthorized access. The OpenAPI Specification (OAS) provides a structured approach to specifying security mechanisms, including authentication and authorization, within APIs. In this article, we'll explore how to leverage the OAS directives for bolstering API security.

Supported Security Schemes

The OAS supports various security schemes, including:

  • HTTP authentication schemes (e.g., basic and bearer types)

  • API keys in headers, query strings, or cookies

  • OAuth 2

  • OpenID Connect Discovery

These schemes can be specified using the securitySchemes directive within the OpenAPI definition.

      type: http
      scheme: basic
      type: http
      scheme: bearer
      type: apiKey
      in: header
      name: X-API-Key
      type: oauth2
          authorizationUrl: ...
          tokenUrl: ...
            read: Grants read access
            write: Grants write access
            admin: Grants access to admin operations

Applying Security Directives

Once the security schemes are defined, they can be applied to specific endpoints or the entire API using the security directive.

      summary: Gets the account billing info
        - OAuth2: [admin]
          description: OK
          description: Not authenticated
      security: []
          description: Server is up and running
          description: Something is wrong

In this example, the /billing_info endpoint is protected with OAuth2 within the admin scope, while the /ping endpoint remains unprotected.

Audit and Remediation

Tools like the 42Crunch VSCode Swagger editor extension enable easy auditing of OpenAPI definitions to detect missing or incomplete security controls. By applying appropriate security directives, developers can address security gaps proactively during the design phase.

Code Generation

Once the OpenAPI definition is audited and validated, developers can leverage code-generation tools like Swagger Codegen or OpenAPI Generator to automatically generate client-side and server-side code. This design-first approach streamlines API development and ensures consistency across implementations.

API Portal

A significant advantage of using the OpenAPI Specification is the ability to generate interactive API portals within applications. These portals allow consumers to explore and experiment with APIs before developing client applications, facilitating easier adoption.

Embracing the Positive Security Model for API Protection

In the realm of API security, the positive security model stands out as a robust approach to ensuring data integrity and protecting against malicious attacks. Unlike the traditional negative security model, which relies on blocklists to identify and block known malicious data, the positive security model operates based on an allowlist principle. In this article, we'll delve into the benefits of leveraging the positive security model, particularly within the context of API development, and explore how the OpenAPI Specification serves as a foundation for implementing this model effectively.

Negative Security Model

Before delving into the positive security model, let's briefly examine its counterpart, the negative security model. In the negative security model, protection tools like Web Application Firewalls (WAFs) maintain a list of known malicious data patterns and attempt to block any requests containing such data. However, this approach suffers from several drawbacks:

  1. Maintenance Overhead: Continuously updating and maintaining the blocklist is labor-intensive and error-prone.

  2. False Negatives: Despite the extensive blocklist, some valid attacks may slip through undetected.

  3. False Positives: Overly restrictive rules may flag legitimate requests as malicious, impacting the application's functionality.

The Strength of the Positive Security Model

The positive security model flips the paradigm by focusing on allowing known valid data while blocking everything else. This approach offers several advantages:

  1. Precision: By defining a precise allowlist, false positives and false negatives are minimized, enhancing the accuracy of threat detection.

  2. Simplicity: Unlike maintaining a blocklist, managing an allowlist is more straightforward and less prone to oversight.

  3. Dependability: With a well-defined contract as the source of truth, the API's behavior becomes more predictable and secure.

Leveraging the OpenAPI Specification

For API development, the OpenAPI Specification serves as the ideal contract for implementing the positive security model. By accurately defining data structures, request parameters, and operations within the OpenAPI definition, developers establish a clear contract for API interactions. This contract becomes the basis for enforcing security controls based on allowing only known valid inputs and operations.

Implementing Positive Security in .NET Core and Java

Let's take a practical approach by implementing positive security measures in both .NET Core and Java using the OpenAPI Specification.

.NET Core Example

// .NET Core API Controller with OpenAPI Specification
public class UsersController : ControllerBase
    private readonly IUserService _userService;

    public UsersController(IUserService userService)
        _userService = userService;

    public ActionResult<UserDto> GetUserById(int id)
        // Implement positive security logic to retrieve user by ID
        // Validate ID against OpenAPI definition
        if (OpenAPISecurityValidator.ValidateRequest(Request, "GetUserById"))
            var user = _userService.GetUserById(id);
            if (user == null)
                return NotFound();
            return Ok(user);
            return Unauthorized();

Java Example

// Java Spring Boot Controller with OpenAPI Specification
public class UsersController {

    private final UserService userService;

    public UsersController(UserService userService) {
        this.userService = userService;

    public ResponseEntity<UserDto> getUserById(@PathVariable int id) {
        // Implement positive security logic to retrieve user by ID
        // Validate ID against OpenAPI definition
        if (OpenAPISecurityValidator.validateRequest(request, "getUserById")) {
            UserDto user = userService.getUserById(id);
            if (user == null) {
                return ResponseEntity.notFound().build();
            return ResponseEntity.ok(user);
        } else {
            return ResponseEntity.status(HttpStatus.UNAUTHORIZED).build();

In both examples, we validate the incoming requests against the OpenAPI definition to ensure that only allowed operations and inputs are processed, adhering to the positive security model.

Conducting Threat Modeling of APIs: A Shift-Left Approach to Security

In the realm of API development, incorporating security measures early in the software development lifecycle is essential for safeguarding against potential threats and vulnerabilities. Threat modeling emerges as a proactive strategy that enables security and development teams to identify, assess, and mitigate potential risks before they manifest into security breaches. In this article, we will explore the concept of threat modeling, its significance in API security, and practical approaches to conducting threat modeling activities using .NET Core and Java.

Threat Modeling

Threat modeling is a systematic approach to identifying potential security threats and vulnerabilities in a system or application. It involves asking critical questions about the system's design, functionality, and potential attack vectors. The key steps in threat modeling can be summarized as follows:

  1. Identify Assets and Scope: Determine the assets being protected and define the boundaries of the system under consideration.

  2. Enumerate Threats: Identify potential threats and vulnerabilities that could compromise the security of the system.

  3. Evaluate Risks: Assess the likelihood and impact of each threat on the system's security posture.

  4. Mitigate Risks: Develop strategies and countermeasures to mitigate identified risks and enhance the system's security.

  5. Review and Iterate: Continuously review and refine the threat model as the system evolves, ensuring ongoing protection against emerging threats.

Importance of Threat Modeling in API Security

Threat modeling plays a crucial role in API security by allowing teams to anticipate and address security concerns early in the development process. By conducting threat modeling activities, organizations can:

  • Proactively Identify Vulnerabilities: By systematically analyzing the system's design and functionality, teams can uncover potential security weaknesses and vulnerabilities before they are exploited by malicious actors.

  • Enhance Collaboration: Threat modeling encourages collaboration between security and development teams, fostering a shared understanding of security risks and promoting a culture of security awareness.

  • Prioritize Security Investments: By prioritizing risks based on their severity and impact, organizations can allocate resources effectively to address the most critical security concerns.

  • Improve Security Posture: Through the implementation of targeted security controls and countermeasures, organizations can strengthen their overall security posture and mitigate potential threats effectively.

Practical Approach: Threat Modeling with .NET Core and Java

Let's illustrate how threat modeling can be integrated into the development process using .NET Core and Java. We'll demonstrate a simplified example of threat modeling for an API endpoint that manages user authentication.

Threat Modeling in .NET Core

// Threat modeling for user authentication endpoint in .NET Core
public class AuthenticationController : ControllerBase
    public IActionResult AuthenticateUser([FromBody] Credentials credentials)
        // Threat modeling considerations:
        // - Potential brute-force attacks on authentication endpoint
        // - Insecure storage of credentials
        // - Lack of input validation on credentials

        // Implement authentication logic

Threat Modeling in Java

// Threat modeling for user authentication endpoint in Java
public class AuthenticationController {

    public ResponseEntity<?> authenticateUser(@RequestBody Credentials credentials) {
        // Threat modeling considerations:
        // - Injection attacks (e.g., SQL injection, XSS) on authentication endpoint
        // - Insufficient authentication controls (e.g., lack of rate limiting, weak password policies)
        // - Exposure of sensitive information in error responses

        // Implement authentication logic

In both examples, we identify potential threats and vulnerabilities specific to the user authentication endpoint, such as brute-force attacks, injection attacks, and insecure storage of credentials. By incorporating threat modeling considerations directly into the code, developers can address security concerns proactively during the development phase.

Automating API Security: Enhancing Development Lifecycle with Automated Tools

Ensuring the security of APIs is a critical aspect of software development, given the myriad of potential vulnerabilities and attack vectors that APIs can be exposed to. However, with the right tools and practices in place, developers can automate security checks throughout the development lifecycle to detect and mitigate potential threats early on. In this article, we'll explore the concept of automating API security and demonstrate practical examples using .NET Core and Java.

Automated API Security

Automating API security involves integrating automated security checks into the continuous integration/continuous deployment (CI/CD) pipeline to identify and address security vulnerabilities in APIs throughout the development process. By leveraging automated tools, developers can detect common security flaws, such as injection attacks, broken authentication, sensitive data exposure, and more, without manual intervention.

CI/CD Integration for Automated API Security

To achieve successful CI/CD integration for automated API security, developers should consider the following key characteristics of security tools:

  • Low Latency of Execution: Security tools should execute quickly to avoid blocking the pipeline for an extended period.

  • Low False Positives: Tools should minimize false positives to prevent unnecessary interruptions in the development workflow.

  • API Accessibility: Tools should provide APIs for seamless integration into CI/CD pipelines, allowing for full automation.

GitHub Actions

GitHub Actions allows developers to define CI/CD pipelines as code and execute them automatically at various stages of the development lifecycle. Below are examples of integrating security tools into GitHub Actions for automated API security checks:

# Example of integrating 42Crunch audit tool into GitHub Actions
name: Security Audit
      - main

    runs-on: ubuntu-latest
      - name: Checkout Repository
        uses: actions/checkout@v2
      - name: Run Security Audit
        uses: 42Crunch/action-security-audit@v1
          apiKey: ${{ secrets.CRUNCH_API_KEY }}


Semgrep is a powerful static analysis tool for detecting security vulnerabilities in code. It offers a rich set of rules for identifying common security flaws. Below is an example of using Semgrep to detect JWT-related vulnerabilities in Java code:

// Example of using Semgrep to detect JWT signature validation failure
public class JWTAuthenticator {
    public boolean authenticate(String token) {
        // Semgrep rule: Look for call to decode() without verify()
        if (token != null) {
            // Decode JWT without verifying the signature
            Jwt decodedToken = Jwt.decode(token);
            return true;
        return false;

Thinking Like an Attacker

In addition to leveraging automated security tools, developers should adopt a proactive approach to API security by thinking like an attacker. By understanding potential attack vectors and exploiting APIs from an adversary's perspective, developers can better identify and mitigate security risks. Here are some practical steps to enhance API security:

  • Equip Yourself with Resources: Explore curated lists of API security resources and tutorials available online.

  • Test Your APIs: Use tools like Postman to interact with your APIs and simulate unauthorized access attempts.

  • Learn by Doing: Work with deliberately vulnerable API applications to gain hands-on experience in identifying and exploiting security vulnerabilities.

  • Learn from Others: Stay informed about recent API breaches and analyze underlying issues to learn from others' mistakes.

By adopting these practices and integrating automated security checks into the development workflow, developers can enhance the security of their APIs and mitigate potential risks effectively.

Exploring OpenAPI Generator for API Code Generation

API code generation is a crucial aspect of modern software development, enabling developers to streamline the creation of server stubs, client libraries, and documentation based on OpenAPI specifications. While SwaggerHub has been a popular choice for generating API code, the open-source community has introduced an alternative solution: OpenAPI Generator. In this article, we'll delve into the capabilities of OpenAPI Generator and demonstrate its usage with practical examples using .NET Core and Java.

Introduction to OpenAPI Generator

OpenAPI Generator, an open-source project, aims to provide a community-driven solution for API code generation. It offers various installation methods, including npm, Homebrew, Docker, and plugins for Maven and Gradle. With OpenAPI Generator, developers can generate server stubs, client libraries, and documentation from OpenAPI specifications seamlessly.

Installing OpenAPI Generator

To install OpenAPI Generator, you can use npm, Homebrew, Docker, or download the JAR file for JVM platforms. Here, we'll focus on using the CLI on MacOS or the Docker image.

Generating Server Stubs

Generating server stubs with OpenAPI Generator is straightforward. You can use a command similar to Swagger Codegen's format:

openapi-generator generate -i book_sample_1.yml -g python-flask -o out/

This command generates a Python Flask project based on the provided OpenAPI specification.

Generating Schema

OpenAPI Generator also allows generating database schema from data definitions within an OpenAPI specification. For example, given a well-specified user entity in the API definition, you can generate a corresponding MySQL schema:

openapi-generator generate -i Pixi.json -g mysql-schema -o out/

This command produces a MySQL script based on the data definitions in the OpenAPI specification.

Generating Documentation

OpenAPI Generator excels at producing human-readable documentation from OpenAPI definitions. You can generate HTML documentation using a command like:

openapi-generator generate -i Pixi.json -g html -o out/

This command generates HTML documentation based on the provided OpenAPI specification.

Using Templates and Custom Generators

One of the powerful features of OpenAPI Generator is its support for templates and custom generators. Developers can customize code generation behavior by modifying templates or creating custom generators from scratch. For instance, you can tweak templates to suit specific requirements or build entirely new language support.

Integration with Frameworks

OpenAPI Generator seamlessly integrates with popular frameworks in various programming languages, facilitating API development and documentation. Let's explore some common scenarios:


For Java APIs, frameworks like Spring Boot and Micronaut offer built-in support for generating OpenAPI documentation. Libraries like Springdoc-OpenAPI and Micronaut OpenAPI provide comprehensive support for generating and customizing API documentation.

.NET Core

In the .NET Core ecosystem, packages like NSwag and Swashbuckle enable the generation of OpenAPI definitions from existing code bases. These packages offer features for producing API documentation and client libraries.


Python developers can leverage packages like apispec for generating OpenAPI documentation. Depending on the chosen framework (e.g., Flask or aiohttp), additional support packages may be required for seamless integration.


For Node.js applications, libraries like swagger-ui-express facilitate the generation and display of OpenAPI documentation. These libraries require an OpenAPI definition for generating documentation.

Object-Level and Function-Level Vulnerabilities in APIs

In the realm of API security, object-level and function-level vulnerabilities pose significant risks to the integrity and confidentiality of data. In this article, we'll delve into these vulnerabilities, understand their implications, and explore strategies to mitigate them using code examples in .NET Core and Java.

Object-Level Vulnerabilities

Object-level vulnerabilities, as defined in the OWASP API Security Top 10, occur when APIs grant access to objects (typically data) not owned by the calling user or client. Despite their severity, addressing these vulnerabilities is relatively straightforward with proper validation mechanisms.

Understanding the Vulnerability

Object-level vulnerabilities often stem from incomplete or improper validation of access rights. For instance, trusting session identifiers, parameters, or JWT tokens without explicit validation can lead to unauthorized access.

Mitigation Strategies

To mitigate object-level vulnerabilities, it's crucial to always explicitly validate access to objects. Let's consider a code sample in Ruby on Rails:

class UserController < ApplicationController
  def show
    if Authorization.user_has_access(current_user, params[:id])
      @this_user = User.find(params[:id])
      render json: @this_user

In this example, Authorization.user_has_access explicitly validates whether the current_user has access to the specified user ID (params[:id]), effectively mitigating the object-level vulnerability.

Practical Implementation

In .NET Core, you can implement similar validation logic in C#:

public class UserController : ControllerBase
    private readonly IUserService _userService;

    public UserController(IUserService userService)
        _userService = userService;

    public IActionResult GetUser(int id)
        if (!_userService.UserHasAccess(HttpContext.User.Identity.Name, id))
            return Unauthorized();

        var user = _userService.GetUserById(id);
        return Ok(user);

Here, UserHasAccess method validates whether the authenticated user has access to the requested user ID before returning the user data.

Function-Level Vulnerabilities

Similar to object-level vulnerabilities, function-level vulnerabilities arise when APIs fail to properly validate access rights for certain operations or endpoints. These vulnerabilities can allow unauthorized users to execute privileged functions.

Understanding the Vulnerability

Function-level vulnerabilities often occur when APIs allow access to high-privilege endpoints without adequate authorization checks. For example, granting access to /admin endpoints without verifying the user's administrative privileges can lead to unauthorized operations.

Mitigation Strategies

Mitigating function-level vulnerabilities involves explicitly validating access rights for privileged endpoints. Let's examine a Python/FastAPI code example:

from fastapi import FastAPI, Depends, HTTPException
from import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

async def get_current_user(token: str = Depends(oauth2_scheme)):
    # Logic to retrieve current user based on token
    return current_user

app = FastAPI()

async def do_admin(current_user: User = Depends(get_current_user)):
    if not AuthZ.user_has_admin_access(current_user):
        raise HTTPException(status_code=401, detail="User does not have admin privileges")
        # Perform admin operations

In this example, the do_admin endpoint checks whether the current user has admin access before executing privileged operations.

Practical Implementation

In .NET Core, you can implement function-level authorization checks as follows:

public class AdminController : ControllerBase
    [Authorize(Roles = "Admin")]
    public IActionResult DoAdminStuff()
        // Perform admin operations
        return Ok();

Here, the [Authorize(Roles = "Admin")] attribute ensures that only users with the "Admin" role can access the /admin endpoint.

Using Authorization Middleware

While implementing authorization checks directly in code can address many vulnerabilities, managing authorization at scale requires robust frameworks. Authorization frameworks abstract policy logic from application code, enabling centralized management and extensibility.

Key Components of Authorization Frameworks

Authorization frameworks typically consist of three key components:

  1. Modeling: Allows designers to define users, groups, roles, and permissions.

  2. Policy Engine: Implements authorization logic based on access requests and policies.

  3. Policy Enforcement: Client library integrated into the application to enforce policy decisions.

Several mature authorization frameworks are available, including:

  • Open Policy Agent (OPA): A Cloud Native Computing Foundation (CNCF) project focused on policy evaluation.

  • Oso: A comprehensive authorization solution supporting various authorization patterns and featuring its own policy definition language (Polar).

  • Casbin: A lightweight authorization framework supporting role-based access control (RBAC), attribute-based access control (ABAC), and more.

Understanding Data Vulnerabilities in APIs: Mitigation Strategies and Best Practices

Data vulnerabilities represent a critical aspect of API security, often leading to breaches and data leakage. In this article, we'll explore the fundamentals of data vulnerabilities, their implications, and effective strategies to defend against them. We'll provide code examples in .NET Core and Java to illustrate key concepts and implementation techniques.

Data Propagation in APIs

Data in APIs traverses through multiple layers, including the request, API layer, and database layer. It's crucial to understand this flow to identify potential vulnerabilities effectively. Here's a simplified architecture diagram:

Three main data processing layers are involved:

  1. Data Input Object: Represents the data format received in API requests.

  2. Database Object: Represents the data format stored in the database.

  3. Data Output Object: Represents the data format transmitted in API responses.

Data vulnerabilities often arise when developers map data directly between these objects without considering data sensitivity.

Excessive Data Exposure

Excessive data exposure occurs when APIs return more data than necessary or desirable, leading to potential security risks. Let's discuss mitigation strategies at both the code and data classification levels.

Coding Securely

Developers should avoid using coalescing operators like to_json() or to_string() indiscriminately, especially with sensitive data. Instead, be explicit about which fields are transmitted in API responses.

In .NET Core, you can define Data Transfer Objects (DTOs) to control data exposure. Here's an example in C#:

public class UserBaseDto
    public string Username { get; set; }
    public string Email { get; set; }
    public string FullName { get; set; }

public class UserInDto : UserBaseDto
    public string Password { get; set; }

public class UserOutDto : UserBaseDto
    // No sensitive data exposed

Classifying Data

Classify data based on sensitivity and intended audience. Review access to APIs based on business needs, adhering to the principle of least privilege. Enhance API test fixtures to monitor data types and flag potential data leakage.

Mass Assignment

Mass assignment occurs when APIs accept more data than intended, potentially allowing attackers to modify sensitive fields. Mitigate this vulnerability by being specific about allowed fields and avoiding implicit assignments.

In Java, you can implement explicit field assignment to prevent mass assignment vulnerabilities. Here's an example using Spring Boot:

public class User {
    private String username;
    private String email;
    private String password;

    // Getters and setters

    public void setPassword(String password) {
        // Explicitly set password after hashing
        this.password = hashPassword(password);

Understanding and Mitigating API Vulnerabilities: Injection, SSRF, Logging, and Resource Consumption

API security remains a critical concern in today's digital landscape, with various vulnerabilities posing significant risks to applications and data. In this article, we'll delve into the realm of injection attacks, SSRF vulnerabilities, insufficient logging, and resource consumption issues in APIs. We'll explore mitigation strategies and best practices, accompanied by code examples in .NET Core and Java.

Injection Vulnerabilities

Injection attacks, such as SQL injection and command injection, exploit systems that trust user input without proper validation. To mitigate these risks, follow these best practices:

Validate User Input

In .NET Core, use parameterized queries to prevent SQL injection:

string query = "SELECT * FROM Users WHERE Username = @Username";
using (var command = new SqlCommand(query, connection))
    command.Parameters.AddWithValue("@Username", userInput);
    // Execute the command

In Java, similarly use parameterized queries with JDBC:

String query = "SELECT * FROM Users WHERE Username = ?";
PreparedStatement statement = connection.prepareStatement(query);
statement.setString(1, userInput);
ResultSet resultSet = statement.executeQuery();

Sanitize User Input

Ensure proper handling of special characters in user input to prevent command injection:

string sanitizedInput = userInput.Replace(";", "").Replace("&", "");
String sanitizedInput = userInput.replaceAll("[;\\&]", "");

Utilize OpenAPI Definitions

Define input formats in OpenAPI definitions to constrain data types and use API firewalls for protection.

Server-Side Request Forgery (SSRF)

SSRF vulnerabilities allow attackers to force servers to make unintended requests. Mitigate SSRF risks with these approaches:

Allow List for URLs

Explicitly define a list of allowed URLs for redirection:

if (allowedUrls.Contains(userInputUrl))
    // Perform the redirection
    // Reject the URL
if (allowedUrls.contains(userInputUrl)) {
    // Perform the redirection
} else {
    // Reject the URL

Restrict URL Schema and Ports

Ensure that only specified URL schemas and ports are allowed for redirection.

Disable HTTP Redirections

Prevent automatic HTTP redirections to untrusted URLs.

Insufficient Logging and Monitoring

Insufficient logging can hinder the detection of abnormal activities and security breaches. Enhance logging and monitoring by:

  • Recording failed operations with transaction details.

  • Identifying suspicious transactions and raising alerts.

  • Integrating API logs into standard SIEM and SOC solutions.

Protecting Against Unrestricted Resource Consumption

Implement rate limiting and throttling to prevent excessive API resource usage:

Rate Limiting

Limit the number of requests per client within a given window:

// .NET Core implementation
services.AddMvc(options =>
    options.Filters.Add(new RateLimitAttribute());
// Java implementation with Spring Boot
public FilterRegistrationBean rateLimitFilter() {
    FilterRegistrationBean registrationBean = new FilterRegistrationBean();
    registrationBean.setFilter(new RateLimitFilter());
    return registrationBean;


Design APIs to gracefully handle variable loads by leveraging cloud-native platforms for automatic scaling.

Understanding Your Stakeholders in API Security

In the realm of API security, understanding the various stakeholders and their perspectives is crucial for effectively managing and implementing security measures. Let's explore the different roles across IT, API, operations, security, and business units, along with their key responsibilities and how they contribute to API security.

Roles in the Security Domain

CISO (Chief Information Security Officer)

  • Responsible for information security in the organization.

  • Ensures that security measures are in place to protect the organization's data and assets.

Head of AppSec

  • Oversees the application security (AppSec) program and activities.

  • Implements security measures to protect applications from vulnerabilities and attacks.

DevSecOps Team

  • Integrates and operates security tools within the automated software development lifecycle (SDLC) environment.

  • Ensures that security is incorporated throughout the development process.

Pentest/Red Team

  • Conducts offensive testing of product releases using black box techniques.

  • Identifies vulnerabilities and weaknesses in the organization's systems and applications.

Risk and Compliance Team

  • Manages risk and compliance in the organization based on applicable operating environments.

  • Ensures that the organization adheres to relevant regulations and standards.

Roles in the Business or Development Domain

CIO (Chief Information Officer)

  • Responsible for the IT operations of a business unit.

  • Oversees the organization's technological infrastructure and strategy.

Product Owner

  • Manages the product development and lifecycle of a business unit's offerings.

  • Defines product requirements and priorities.

Technical Lead

  • Manages the technical team responsible for developing and maintaining products.

  • Provides technical guidance and support to team members.

Solution Architect

  • Supports and evangelizes the product to customers.

  • Designs and implements technical solutions that align with business goals.

DevOps Team

  • Operates the build and release process through automation.

  • Facilitates collaboration between development and operations teams.

Roles in the API Product Domain

API Product Owner

  • Manages the product management of a set of APIs offered as a product.

  • Defines the roadmap and strategy for API products.

API Platform Owner

  • Owns the central API platforms (e.g., API gateways, management portals) and API PaaS infrastructure.

  • Ensures the reliability and security of API platforms.

API Architect

  • Defines the overall API strategy, including authentication, authorization, and architecture.

  • Designs APIs to meet business and technical requirements.

Distributing Ownership of API Security

Ownership of API security may reside across multiple organizational units, each responsible for different aspects of security implementation. For example:

  • The API platform owner may focus on applying API gateway policies.

  • The API architect may handle overall authentication strategy.

  • The head of AppSec may oversee SAST/DAST scans.

  • The CISO holds ultimate accountability for API security.

To avoid duplication of responsibilities and ensure effective security management, roles and responsibilities should be clearly defined and distributed among stakeholders. By involving various stakeholders and aligning their efforts, organizations can achieve a comprehensive and robust approach to API security.

The 42Crunch Maturity Model for API Security

As a technical evangelist at 42Crunch, I developed a comprehensive six-domain API security maturity model aimed at assisting organizations in assessing their current security posture and charting a roadmap towards a more secure environment. This model has gained popularity among customers due to its structured approach and actionable insights.

Overview of the Maturity Model

The maturity model consists of six key domains, each representing a crucial aspect of API security. Within each domain, specific activities are outlined, categorized based on their maturity level: non-existent, emerging, or established. Let's delve into each domain:

1. Inventory

Maintaining an up-to-date and accurate inventory of APIs is fundamental for visibility into the organization's risk and attack surface. Key activities include:

  • Introduction and tracking of new APIs

  • Discovering API inventory from source code repositories

  • Runtime discovery of APIs through network traffic inspection

At lower maturity levels, only a basic inventory is maintained, often via manual tracking. As maturity increases, a centralized platform is utilized, and shadow/zombie APIs are actively managed.

2. Design

Addressing security issues at the design phase is cost-effective and crucial for building secure APIs. Key elements of secure API design include:

  • Authentication methods

  • Authorization models

  • Data privacy and exposure requirements

  • Compliance considerations

  • Threat modeling exercises

Lower maturity levels may lack a formal design process, while higher levels emphasize security as a first-class element of API design, incorporating standard practices like threat modeling.

3. Development

The development phase is where specifications are implemented, making it vital to follow security best practices. Key considerations include:

  • Choice of languages, libraries, and frameworks

  • Correct configuration of frameworks

  • Defensive coding practices

  • Central enforcement of authentication and authorization

At lower maturity levels, developers may be unaware of security concerns, while higher levels see proactive adoption of secure coding practices.

4. Testing

Effective API security testing is essential to identify vulnerabilities before deployment. Key aspects of testing include:

  • Authentication and authorization bypass testing

  • Data exposure and handling of invalid requests

  • Rate limiting and quota enforcement

  • Integration with CI/CD processes

Lower maturity levels may lack specific API security testing, while higher levels tightly integrate testing into all stages of the SDLC.

5. Protection

Despite efforts in earlier stages, APIs remain susceptible to attacks and require dedicated protection mechanisms. Key aspects of protection include:

  • JWT validation

  • Secure transport options

  • Brute-force protection

  • Logging and monitoring of protection mechanisms

Lower maturity levels may rely solely on standard firewalls, while higher levels implement dedicated API firewalls for enhanced protection.

6. Governance

A robust governance process ensures that APIs are developed and maintained according to organizational standards. Key principles of governance include:

  • Consistency in API usage

  • Standard processes for API development and testing

  • Compliance with data privacy requirements

  • Lifecycle management of APIs

Lower maturity levels may lack standardized processes, while higher levels enforce proactive governance and address deviations.

Planning Your Program

Establishing clear objectives and understanding the motivations behind implementing an API security program are crucial first steps. Organizations should prioritize APIs based on their security objectives and gradually expand their program.

Assessing Your Current State

Assessing the current state involves estimating API inventory, determining ownership, and mapping capabilities to the maturity model. It's essential to build consensus among stakeholders and establish controls and procedures to meet security requirements.

Building a Landing Zone for APIs

Creating secure landing zones with integrated security tooling simplifies the development process and ensures consistent security across APIs. Organizations can standardize landing zones to achieve greater API security.

Building Your Teams

Building a successful API security team requires individuals with diverse skills and backgrounds, emphasizing diplomacy and collaboration over technical specialization. Leveraging security champions within development teams can also enhance security efforts.

Tracking Your Progress

Selecting key performance indicators (KPIs) aligned with program objectives helps track progress effectively. Understanding the nature of KPIs and selecting metrics based on authentication, authorization, and coverage metrics can drive continuous improvement.

Integrating with Existing AppSec Programs

Aligning API security initiatives with existing DevSecOps teams and integrating API testing methods into security testing processes enhances overall security efforts. Understanding API dependencies and managing software dependencies are also critical aspects.


  • Defending APIs by Colin Domoney